Eu nunca cobri o meu e este artigo também parece recomendar não abordá-lo:
Your central air conditioning unit consists of a compressor and condensing unit placed outdoors in a metal housing. These units, built to resist the weather, generally do not need a cover. In fact, covers can cause problems because they trap moisture and create an inviting winter home for small animals.
Professionals who service the units tell me that most of the damage they see in spring was caused by rodents living in the units and chewing on wiring.
If your air conditioner is subject to falling ice or other debris, you could cover its top with a piece of plywood, plastic or metal held in place by a weight.
Reference: http://misterfix-it.com/blog/?page_id=36#cac
Eles fazem questão de que uma capa proporcione uma casa de inverno perfeita para os animais, o que causaria danos ao seu ar-condicionado.